Birds migrating all over the world has been something that has confused us in history and now amazes us. Although migration is still not completely understood, over the previous few decades we have managed to learn a lot more. Ringing birds was the first key to finding out where they go and now with new age technology like transmitters and satellites, even more so.
Migrate was derived from the Latin word, migrare, which means, “to move from one place to another”. It can be described as predictable journeys, usually from breeding or food sources, to non-breeding areas and back again. In Southern Africa alone, there are more than 130 bird species, either migrating within the African continent itself, or leaving and going into Europe or Asia.
Why migrate?
Like people going on a vacation to get away from the cold, birds follow the same sort of pattern. Why stay somewhere cold, with no or little food, when you can fly into another hemisphere and have the best of both worlds as to say? The main issue is, the distance that needs to be traveled, the energy usage in between and high risk doing this twice a year. With all the risks involved, the bird needs to figure out if food and weather are worth the trip. For some species it just simply isn’t worth it, but for others it improves their chance of survival and better chance to raise their young.
Most of the migration issues come down to food. This means that most of your migrants are insect eating birds, like swifts, swallows, bee-eaters and nightjars. With warm weather and rain, insects will be plentiful and so this is where the birds go. This is also why a lot of our wading birds, like Greenshanks and sandpipers come down, when their invertebrate prey is more abundant. When Autumn arrives and food numbers start to go down, birds know it is time to leave.
Where to go?
People hear the word migration and immediately think that birds always leave the continent, but this is not always the case. Some birds migrate, but only within the African continent itself, these are known as intra-African migrants. Most of these birds follow the rains, going between the two hemispheres or hanging close to the equator. Whilst most species will only breed once a year, there are some species, like Diedrik’s and Red-chested cuckoo that will breed twice, in both of their holiday destinations. As they’re cuckoo’s and don’t raise their own, it makes sense as they’re cuckoo’s don’t expend as much energy raising chicks.
Then there are the species that jump the continent, these are known as Palaearctic – African migrants. These are the birds that have the most difficult trip as they can travel thousands of kilometres or miles. These birds are generally non-breeding migrants in Africa and do most of their breeding in the north. They escape their northern breeding grounds that get eaten up by snow and ice, moving to Africa to enjoy the food and better weather. Waders, Barn swallows, White Storks and Common Buzzards are good examples of this.
Some birds species will even just migrate within their own country. These birds will often be known as Altitudinal migrants. These birds well spend the summer time around the mountains or high grasslands, perfect for breeding time in summer. They then move down to the lower altitudes for the winter time, enjoying the warmer weather and more stable weather conditions. African Stonechat is the perfect example of this.
Rest, refuel and route
Over time, birds have figured out the best routes to travel, to and from their destinations of choice. Distance, mountain ranges, wind patterns, places to stop and rest and even whether they flap or soar, all had to be taken into consideration. Places to stop, rest and feed are very important. Flying those sort of distances consumes mass energy and so would not be possible in a single flight. Just like an aircraft, they need to refuel. Many species have stop over sites that have been used for decades or even centuries, obviously passed down generationally.
Crossing an ocean is something that all of these birds try and avoid. It isn’t always possible, especially shorter crossings, but long crossings are avoided completely. This means that at some narrow crossings between large land masses, birds are funnelled. Mass amounts of birders will head twice a year head towards Israel and Gibraltar to watch this. Your large birds like storks and birds of prey rely heavily on the land as they need thermals for their flight.
How do they find their way?
A major question with regard to migration, is whether young are taught how and where to go, or whether they just know? From what studies have now shown, is that it is built in. Youngsters that have been observed, leaving an area earlier, or later than their parents, still manage to end up in the right place. This is not to say that experience is not important, as older birds adapt easier if there are any changes necessary to the original route plan.
Three compasses may be used by birds, a magnetic, sun and star compass. It is thought that birds have small traces of metal elements and so allows them to respond to magnetic pulls at the pole. Birds along with other animals quickly learn to use the rising and setting sun. Birds can pick up on ultra-violet light and so can see the direction of the sun even on overcast days. Birds also know there constellations and studies have shown that birds can fly at night, orientating themselves with certain stars.
In the end, incredible as it may seem, these feathered friends, manage to travel across the world and across continents. All by themselves, they manage to fly from one hemisphere to the other. They head straight back to either good feeding grounds or nests sites, knowing exactly where to go, months after their previous visits. Hopefully one day, we will understand exactly why, but for now, we have some pretty good ideas.
